Miners at the Winsford mine in Cheshire. Its owners have failed in legal attempts to get detailed geological information relating to an underground gas storage facility proposed by GDF Suez. Photograph: Christopher Thomond for the Guardian
Christopher Thomond/Guardian

Britain's biggest and oldest salt mine, where lorries queue up for grit whenever snow and ice are forecast for Britain, is fighting a last-ditch battle against plans to store pressurised gas in caves less than a mile away.

The owners of the 160-mile warren of tunnels at Winsford rock salt mine in Cheshire – which house priceless items from the National Archives as well as turning out grit – have failed in their legal efforts to acquire detailed geological information relating to an underground gas bunker at nearby Stublach.

The bunker is being proposed by the French energy firm GDF Suez. Staff at the salt mine fear that any gas leak from the facility would be disastrous.

GDF Suez's Storengy storage division has a good safety record, but the US-owned Salt Union company at Winsford says that gas storage does not sit easily alongside such a large and busy mine, where employees work 24 hours a day throughout the year.

"The scale of what could happen if there was any leak could be disastrous," said Harold James, managing director of Compass Minerals UK, Salt Union's parent firm, during a three-hour tour of the labyrinth where more than 1.4m tonnes of rock salt is extracted by machines a year. "We have 50 people here, known to all of us, underground round the clock, seven days a week. No business interest should supersede their safety."

Confidential government files and National Archives material are also stored in the mine Christopher Thomond/Guardian

The mine is an intensely active place. Colossal machinery was taken into the mine in pieces – like steamers bound for African lakes during the days of British imperialism – then reassembled underground. One piece is a new £2.5m continuous cutting machine that eats through the rock, another is a bulldozer with a bucket that carries 25 tonnes of shattered salt.

Petrol-driven equipment is banned and extra security measures apply to the miles of shelves in the archive section, where documents dating back to Tudor times are stored, alongside confidential police records, celebrated architectural models and a hoard of other material.

The salt was laid down 220m years ago when this part of Cheshire was under first the sea, then a briny inland lagoon. Deep mining below 150 metres (492ft) began in the 1840s and was so intense that 65 firms fought for trade until combining as the Salt Union.

The Storengy gas project has been four years in the making and Salt Union has been campaigning against it for three of them, during which time it has made requests, issued a lawsuit and produced vivid leaflets showing flames pouring into the mine from fissures in the rock.

During the 1.5m construction man-hours spent at Stublach since 2008 there has been only one "lost time" injury – a worker's trapped thumb in April of that year – and the operation is regularly monitored by safety experts.

Anxiety has grown about geological unpredictability where the salt strata have been mined since Roman times. A landslip between the Winsford and Stublach sites thousands of years ago left the salt strata lower on the Stublach side.

Winsford's mine manager, Gordon Dunn,, who has years of experience in less stable Yorkshire coalfields, said: "Were any gas to leak underground, it would naturally seek the surface, and cracks and fissures could take it to the fault and then upwards – to our side."

Graham Evans, the Tory MP for Weaver Vale, is pressing the Department of Energy and Climate Change (Decc) and the HSE for extra research and an audit of the planning system for underground schemes after Winsford was left out of the consent loop because the surface buildings of the two sites were far apart.

"I find it incredible that Salt Union was not initially consulted," said Evans, "and it seems extraordinary that they have been obliged to go to the Freedom of Information [FOI] Act to try to get reassurance."

The firm applied for judicial review of the standard HSE procedures in the case last summer but a judge said further independent checks were unnecessary. It then had to make FOI applications for geological material.

Evans added: "I can imagine what would happen if we had a gas storage facility in place and someone then applied to mine 800 metres away. The [HSE] does an excellent job and quite rightly applies famously strict standards to anything which might be dangerous. It is only one step further to recognising that the 'accident waiting to happen' possibilities here, however remote, are potentially enormous."

The Conservative MP for neighbouring Eddisbury, Stephen O'Brien, is also pressing for more details after the employment minister Mark Hoban stonewalled Commons questions. Hoban repeatedly said the Stublach caverns had passed secure storage tests, and would not be drawn on wider strata issues in the event of an escape.

Storengy said it had followed the regulatory process and was working closely with the relevant authorities. It added that natural gas had been stored without reported incident in the Cheshire salt layers for many years and that the suitability of the area's geology had been confirmed.

The HSE does not have powers to rate a particular hazard as exceptional beyond the huge range covered in its official remit.

An HSE spokesman said: "Underground gas storage of this type is common in continental Europe and several such sites are already operational in the UK with several more likely to come on line in the next few years.

"We are assessing the pre-operational safety report [from] Storengy."

Decc said the safety considerations were a matter for the HSE and the department would not intervene.

But pressure is expected to continue at a time when ministers are also dealing with plans to store nuclear waste in Cumbria – possibly beneath the Lake District national park – which has raised similar "exceptional case" issues.